FIG. 1 shows a system building example assuming that a 3G mobile network system is built by using the 2nd and 2.5th generations (2/2.5G) network systems without performing network sharing.
In the system shown in FIG. 1, assuming that communications are performed among 3G subscriber terminals (mobile telephone terminals) 11, 21 and 31 that mainly belong to respective 3G mobile network systems 10, 20 and 30 that are individually built by three different carriers (providers), in a case where the terminal 11 performs communication with the terminal 12, a call transmitted from the terminal 11 is, for example, received by a base station radio apparatus 12 of the carrier 10, and transmitted to a base station control apparatus 13. Then, the call is transmitted to a mobile switch center 24 via: a mobile switch center 14; a mobile communication network 15 of the carrier 10; a public telephone network PSTN; and a mobile communication network 25 of the carrier 20. Thereafter, the call is connected to the terminal 21 via a base station control apparatus 24 and a base station radio apparatus 23.
In a case where the system as mentioned above is assumed, since the 3G systems are separately built by the respective carriers, enormous business investment is required in total. In order to solve such a problem, a concept of so-called network sharing has been proposed in which a mobile communication network is shared among a plurality of carriers.
FIG. 2 shows an example in which a 3G mobile communication network is built by using a known network sharing method. According to the network sharing method, base station radio apparatuses 111 through 114 and base station control apparatuses 121 and 122, for example, are shared among a plurality of carriers. The carriers may build, on their own, mobile switch centers (MSC) 14, 24 and 34, and serving GPRS (global packet radio service) support nodes (SGSN) 16, 26 and 36, in addition to the mobile communication networks 15, 25 and 35 and application servers 17, 27 and 37, respectively. Fundamentally, communication resources that should be built by each of the carriers are limited to those parts relating to: e.g., use conditions of each user, which should be directly managed by each of the carriers; counting of usage fees; and its own specification (know-how).
It should be noted that, here, “a method of sharing only a RAN (radio access network; a network including RNCs, base station radio apparatuses, and terminals) part” is adopted, and routing is performed from the shared RNCs 121 and 122 to the MSCs 14, 24 and 24 and the SGSNs 16, 26 and 36 for the respective carriers in accordance with the kinds of carriers to which terminals (MS) subscribe.
In addition, depending on the size of the network, the MSC and the SGSN are finely classified as shown in FIG. 3: (MSC=MSC+GMSC (gateway mobile switch center)+HLR (home location resister)&EIR; SGSN=SGSN+GGSN (gateway GPRS support node)). However, here, for simplicity, only the MSC and the SGSN are shown as the minimum system image.